Motion Blur

Provides the sense of an increase in speed of movement in a scene or for a character.

Why Motion Blur is necessary

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Motion Blur

The artificial look of some computer graphics was discussed previously in the section on Depth of Field effects(URL) , however there is another reason why computer graphics look this way.

Real-time graphics are moving images, in other words, they are movies. On the other hand, the individual images are still images. For example, a CG movie has a frame rate that is 60 frames/second, one second of a movie is composed of 60 frames shown one after the other.

The real world, in contrast, can be seen as a series of images, one after the other with an infinite frame rate. CG movies, with their limited frame rate, therefore have a different appearance to that of the real world. Arguably this is one of the reasons that CG looks artificial.

In the real world, where the frame rate is infinite, any speed can be expressed, however, speed beyond a certain limit is perceived as a blur to the human eye. This is understandable since the human perception of speed (speed at which the brain can perceive what is seen by the eye) is not that fast.

The human eye is able to open and close rapidly, i.e. blinking, however this does not fulfill the same function as the shutter on a camera. Generally speaking, the human eye continuously captures the images that it sees, but any object that moves faster than its ability to perceive is seen as only as part of the path of motion and thus appears as a blur.

If this is the case, there should be no problem even if a person with a slower perception sees a CG movie with limited frame rate. However objects on the still images (each frame) that make up a CG movie are drawn completely still. We could say that the frames that make up the CG movie were taken with a camera that has a shutter speed of 1/∞ or, in other words, roughly zero. Naturally no such camera exists in the real world, and even if the shutter speed of an actual camera was increased to this extent, the image captured would be completely black.

This is probably another reason that CG images appear artificial. This is where the Blur effect becomes useful.

Raising the frame rate of CG to an infinite number is not possible, however if the track of the motion to the destination position which should be drawn on the following frame is drawn in one frame, it is a simple matter to draw the movement that should be displayed in the time between the frames. To put it a different way, while maintaining a limited frame rate, and drawing all movements of the moving body, it is possible to approach a quasi but near limitless frame rate.

If the movement track of a moving body is shown at greater than the speed of human perception, the scene actually appears as if it were captured with a slow shutter speed, but is actually a CG with a shutter speed of 1/∞.

This kind of blur effect added to the track of a fast moving body is referred to as Motion Blur.

While Motion Blur is an effective way to show natural movement of a moving body in a CG image, it is also effective in augmenting characteristically choppy flip book-like movements and making them appear smoother. The latter is particularly useful for variable frame rate real-time graphics.

YEBIS also supports Object Motion Blur

The first is a Motion Blur that uses a velocity map to output the speed vector of an object in the scene in pixel units and generates the blur. This blur effect is also referred to as an Object Motion Blur (OMB) and performs a meticulous blur effect on the object in unit parts. For example, it can do an accurate blur on a warrior running and swinging his sword even when the running movement and the sword swinging movement are done at different speeds and in different directions. This blur effect is not only effective for expressing speed and dynamic movements, it is also highly effective in improving the ease with which the track of moving object can be followed.

The other type of effect is Camera Blur. This is a blur effect used when the viewpoint itself has moved and causes a blur in the entire image. This is an effective way to create powerfully realistic ambience, as if a camera has been placed directly into the virtual space.

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